This invention relates to inkjet printers and, more particularly, to a monolithic printhead for an inkjet printer.
Inkjet printers typically have a printhead mounted on a carriage that scans back and forth across the width of a sheet of paper feeding through the printer. Ink from an ink reservoir, either on-board the carriage or external to the carriage, is fed to ink ejection chambers on the printhead. Each ink ejection chamber contains an ink ejection element, such as a heater resistor or a piezoelectric element, which is independently addressable. Energizing an ink ejection element causes a droplet of ink to be ejected through a nozzle for creating a small dot on the medium. The pattern of dots created forms an image or text.
Additional information regarding one particular type of printhead and inkjet printer is found in U.S. Pat. No. 5,648,806, entitled, xe2x80x9cStable Substrate Structure For A Wide Swath Nozzle Array In A High Resolution Inkjet Printer,xe2x80x9d by Steven Steinfield et al., assigned to the present assignee and incorporated herein by reference.
As the resolutions and printing speeds of printheads increase to meet the demanding needs of the consumer market, new printhead manufacturing techniques and structures are required.
Described herein is a monolithic printhead formed using integrated circuit techniques. Thin film layers, including a resistive layer, are formed on a top surface of a silicon substrate. The various layers are etched to provide conductive leads to the heater resistor elements. Piezoelectric elements may be used instead of the resistive elements.
At least one ink feed hole is formed through the thin film layers for each ink ejection chamber. In one embodiment, a protective layer is deposited over the ink feed hole area.
An orifice layer is formed on the top surface of the thin film layers to define the nozzles and ink ejection chambers. In one embodiment, a photo-definable material is used to form the orifice layer.
A trench mask is formed on the bottom surface of the substrate. A trench is etched (using, for example, TMAH) through the exposed bottom surface of the substrate. The trench completely etches away portions of the substrate beneath the ink feed holes. The protective layer prevents the TMAH from etching the substrate from the front side through the ink feed hole.
The protective layer is then removed, and a second trench etch is performed. The TMAH solution etches away the substrate portion exposed through the ink feed holes. The second trench etch inherently aligns the edge of the trench with the ink feed holes. This two-step trench etch eases the tolerances for the trench mask and results in a precisely positioned trench, since the trench side walls are ultimately aligned to the thin film openings.
In another embodiment, a separate protection layer is not deposited. Instead, a field oxide (FOX) layer, formed over the substrate as one of the thin film layers, is used for protection. The ink feed holes are etched through the thin film layers down to the FOX layer. A first trench etch is conducted as in the previous embodiment. The portions of the FOX layer in the ink feed hole areas are removed with a buffered oxide etch. A second trench etch is then performed that self-aligns the trench sidewalls to the thin film openings. This process is more economical than the previous embodiment using a separate protection layer.
The resulting fully integrated thermal inkjet printhead can be manufactured to a very precise tolerance since the entire structure is monolithic, meeting the needs for the next generation of printheads.
The process may be used to form openings in devices other than printheads.